In-situ X-ray absorption spectroscopy study on the formation of superoxides on Cu x Sn y composite catalysts enables the direct synthesis of catechol

This work proposes the activated mechanical alloyed composite catalysts by in-situ O 2 heat treatment (Cu x Sn 100−x O 2 HT). The catalytic activity of catalysts is improved tremendously for the phenol hydroxylation by superoxide (O 2 − ). The conversion is almost 100% and selective to 94% catechol (CAT). To understand the formation of superoxide, in situ time-resolved Cu K-edge and Sn L 3 -edge X-ray absorption spectroscopy explain the contribution of an oxygen atom to the Cu x Sn y composites. Meanwhile, in-situ XAS with O 2 heat treatment depicts how superoxide bonded on Cu x Sn y composites. Quantitatively, H 2 -TPR and curve fitting ATR-FTIR determine the total amount of superoxide on MAed Cu x Sn 100−x O 2 HT and distinguish the numbers of O 2 − on Cu and Sn sites in Cu x Sn 100−x O 2 HT. EPR explains that the hybridization of d-orbitals of Cu 2+ and p-d orbitals of Sn 4+ shifted the g-factor of a free electron in superoxide. XPS depth profiling of O 1s reveals identical superoxide on the composite Cu x Sn y O 2 HT catalysts. After optimizing the Sn contents, Cu 30 Sn 70 O 2 HT exhibits the highest catalytic activity and a number of superoxides, giving the CAT 183 μmol in conjunction with reducing tar contents. Extended X-ray absorption fine structure (EXAFS) illustrates the present compressive strain of Cu–O distance and is essential in increasing the quantity of CAT. The work presents how mechanical alloying can be a potential free-solvent catalyst synthesis.